Preheat your oven to 200°C (390°F) and line a baking sheet with parchment paper.
Thaw the puff pastry sheets at room temperature for about 15 minutes until they are pliable but still cold.
In a skillet, heat a tablespoon of olive oil over medium heat, then add the minced garlic and cook until fragrant, about 30 seconds.
Add the chopped spinach to the skillet and cook until wilted and moisture has evaporated, about 2-3 minutes. Let it cool slightly as it might be hot and moist.
In a bowl, combine the grated cheese, cooled spinach mixture, a pinch of nutmeg, and season with salt and pepper. Mix until evenly combined, creating a flavorful filling.
Unfold the puff pastry sheets onto a lightly floured surface and roll gently to even out the creases, increasing their size slightly.
Cut each sheet into 9 equal squares, about 10x10 cm (4x4 inches), using a sharp knife or pizza cutter.
Place a teaspoon of filling in the center of each square, then fold the corners into the middle to form a pinwheel or leave as a square, sealing edges with a little water if needed.
Arrange the filled puffs on the prepared baking sheet, spacing them about 2 cm apart. Brush the tops with beaten egg for a shiny, golden finish.
Bake in the preheated oven for 20-25 minutes, until golden brown and crispy, with cheese bubbling inside and layers puffed up.
Remove from oven and let rest for 5 minutes on a wire rack to set the filling and enhance crispness. Serve warm and enjoy the flaky, cheesy bites.
